The invention relates to layer systems having at least one layer comprising titanium aluminum oxide. The layer comprising titanium aluminum oxide may be either a functional layer--with or without interruption by an intermediate layer which is optically inactive--or a functional layer formed from a metal oxide which is interrupted by an intermediate layer comprising titanium aluminum oxide. The layer systems are structurally and thermally stable at operating temperatures of over 600.degree. C. The layer systems may either comprise only one functional layer or may be a multilayer system, preferably an alternating layer system composed of functional layers with high and low refractive indices.